Aqueous nanospheres self-assembled from hyperbranched polymers and silver ions: Molecular inclusion and photoreduction characteristics

Hyperbranched polymers with (N,N-diethylamino)dithiocarbamoyl (DC) units as peripheral groups (HBP-DC) spontaneously form nanospheres in aqueous silver nitrate. Although HBP-DC itself is insoluble in water, coordination of Ag(I) ions to surface DC units imparts cationic charges which make Ag(I)/HBP-DC complexes dispersible in water and drive their self-assembly into nanospheres. These Ag(I)/HBP-DC complexes show binding of hydrophobic guest molecules in the course of self-assembly. When mixtures of tetraphenylporphyrin (TPP) and HBP-DC in THF are added to aqueous silver nitrate, intense fluorescence of TPP was observed. As TPP molecules form nonluminescent aggregates when injected in water, the luminescence observed in aqueous Ag(I)/HBP-DC nanospheres indicates that TPP molecules are confined in the hydrophobic interior of aqueous nanospheres. The surface of Ag(I)/HBP-DC nanospheres, meanwhile, serve as scaffolds to produce silver nanocrystals. The Ag(I)-DC complexes formed on the surface of Ag(I)/HBP-DC nanospheres undergo photoreduction, which give small silver nanocrystals evenly distributed on nanospheres. The size and density of silver nanocrystals are tunable depending on the reaction condition. The coordination-assisted self-assembly of HBPs provides a simple and useful means to develop aqueous nanospheres whose interior and exterior surfaces are readily modifiable. It offers up considerable possibilities for their application as polymer-inorganic integrated vessels.